The Yak-9 (NATO code 'Frank') was the most numerous Soviet fighter of WWII, with 16,769 built between 1942 and 1948. The Yak-9U variant employed many of the design improvements proved on the Yak-3, the result being a very similar appearance. Fitted with a Klimov VK-105PF2 engine and plywood fuselage covering (earlier Yak-9s used fabric), this was one of 200+ Yak-9s flown by the Bulgarian Air Force. Withdrawn from service in late 1952 and now preserved at the superb Krumovo museum.